Organic electroluminescent display device

ABSTRACT

An organic EL display device of active matrix type wherein insulated-gate field effect transistors formed on a single-crystal semiconductor substrate are overlaid with an organic EL layer; characterized in that the single-crystal semiconductor substrate ( 413  in FIG.  4 ) is held in a vacant space ( 414 ) which is defined by a bed plate ( 401 ) and a cover plate ( 405 ) formed of an insulating material, and a packing material ( 404 ) for bonding the bed and cover plates; and that the vacant space ( 414 ) is filled with an inert gas and a drying agent, whereby the organic EL layer is prevented from oxidizing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device having a circuitbased on insulated-gate field effect transistors in which asingle-crystal semiconductor is used for an active layer, and a methodof fabricating the semiconductor device. More particularly, the presentinvention is well suited for applications to an electrooptic devicewhich is typified by an organic electroluminescent display devicewherein the same substrate is overlaid with a pixel unit and drivercircuits disposed around the pixel unit, and to an electronic apparatusin which the electrooptic device is installed. Incidentally, here inthis specification, the expression “semiconductor device” is intended tosignify general devices which function by utilizing semiconductorproperties, and it shall cover within its category the electroopticdevice and the electronic equipment including this electrooptic device.

2. Description of the Related Art

In the field of flat display devices (flat panel displays) typified byliquid-crystal display devices, organic EL (electroluminescent) displaydevices, etc., there has been known technology wherein a display deviceof active matrix type is fabricated by employing insulated-gate fieldeffect transistors (hereinbelow, the “field effect transistors” shall beabbreviated to “FETs”) formed on a single-crystal semiconductorsubstrate. Unlike in a case where a display device of active matrix typeis fabricated by forming thin-film transistors (hereinbelow, abbreviatedto “TFTs”) on a glass substrate or a quartz substrate, the technologyhas had the advantage that techniques fostered in the field oflarge-scale integrated circuits (LSIs) are applicable as they are, andthat the FETs of high performance which are capable of low-voltage driveat high speed can be integrated and formed at a high density on thesubstrate. On the other hand, however, it has been considered thedisadvantage of the technology that the display device is restricted toone of reflection type or spontaneous luminescence type because thesubstrate is opaque to visible light, or that the single-crystalsemiconductor substrate is restricted to sizes available on the market.

In the technological trends toward higher image quality and fulldigitization in the field of the display devices, the enhancements ofperformances required of the active matrix type display device haveinevitably heightened. The active matrix type display device is soconstructed that transistors (such as TFTs or FETs) in the number ofseveral tens to several millions are arranged in a pixel unit fordisplaying an image, and that pixel electrodes are respectivelyconnected to the transistors. In operation, the image is displayed insuch a way that voltages to be applied to respective pixels arecontrolled by the switching functions of the corresponding transistors,whereby some of EL elements are caused to luminesce. In the organic ELdisplay device, when the switching transistors disposed in therespective pixels are turned ON, currents are caused to flow throughcurrent controlling transistors by signals generated in accordance withimage data, whereby the EL elements luminesce spontaneously.

However, an organic EL layer which serves as the basic portion of theorganic EL display device is very liable to oxidize, and it easilydeteriorates in the presence of a slight amount of oxygen. Besides, ithas a low resistance to heat, and this also is a factor promotingoxidation. The liability to oxidize is the cause of a short lifetime ofthe organic EL element, and has formed a serious obstacle in puttingthis element into practical use.

SUMMARY OF THE INVENTION

The object of the present invention is to overcome the problem as statedabove, and to provide an organic EL display device of high reliability.

Another object of the present invention is to provide an electron devicewhose display unit is highly reliable, by adopting such an organic ELdisplay device for the display unit.

The construction of the present invention for accomplishing the objectsconsists in an organic EL display device of active matrix type whereininsulated-gate field effect transistors formed on a single-crystalsemiconductor substrate are overlaid with an organic EL layer;characterized in that the single-crystal semiconductor substrate is heldin a vacant space which is defined by a bed plate and a cover plateformed of an insulating material and a packing material for bonding thebed and cover plates; and that the vacant space is filled with an inertgas and a drying agent.

Also, the construction of the present invention consists in an organicEL display device of active matrix type having a pixel unit whereininsulated-gate field effect transistors formed on a single-crystalsemiconductor substrate are overlaid with an organic EL layer;characterized in that the single-crystal semiconductor substrate is heldin a vacant space which is defined by a bed plate and a cover plateformed of an insulating material, and a packing material for bonding thebed and cover plates; that the cover plate is formed of a transparentmember in its area which lies over the pixel unit; and that the vacantspace is filled with an inert gas and a drying agent.

A single-crystal silicon substrate can be favorably employed as thesingle-crystal semiconductor substrate. Besides, the vacant space shouldpreferably be filled with an inert gas selected from the groupconsisting of helium, argon, krypton, xenon and nitrogen, and a dryingagent selected from the group consisting of barium oxide and silica gel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an organic EL display device of activematrix type;

FIGS. 2(A) and 2(B) are diagrams showing the top plan structure andcircuit arrangement of a pixel unit in the organic EL display device,respectively;

FIG. 3 is a top plan view of the active matrix type organic EL displaydevice;

FIG. 4 is a sectional view showing the internal construction of theorganic EL display device;

FIG. 5 is a perspective view showing the construction of a goggle typedisplay device in which the organic EL display devices are installed;and

FIGS. 6(A) and 6(B) are sectional views of the goggle type displaydevice in which the organic EL display devices are installed.

PREFERRED EMBODIMENTS OF THE INVENTION

First, an organic EL display device according to the present inventionwill be described with reference to FIG. 1. The organic EL displaydevice according to the present invention has such a structure that apixel unit and driver circuits around the pixel unit are disposed usingfield effect transistors (FETs) of insulated gate type which are formedon a single-crystal semiconductor substrate (for example, single-crystalsilicon substrate).

A substrate 101 is made of single-crystal silicon having a comparativelyhigh resistance (for example, one of n-type at about 10 [Ωcm]), and ap-well 102 and n-wells 103˜105 are formed in self-alignment therein.Adjacent FETs are isolated by a field oxide film 106. In forming thefield oxide film 106, channel stoppers may be formed by introducingboron (B) into the selected parts of the substrate 101 in accordancewith ion implantation.

Gate insulating films 110, 116, 122 and 128 are formed by thermaloxidation. Gates 111, 117, 123 and 129 consist of polycrystallinesilicon layers 111 a, 117 a, 123 a and 129 a formed from apolycrystalline silicon film deposited to a thickness of 100˜300 [nm] byCVD, and silicide layers 111 b, 117 b, 123 b and 129 b formed thereon toa thickness of 50˜300 [nm], respectively. The polycrystalline siliconlayers may be doped with phosphorus (P) at a concentration of 10²¹[/cm³] or so beforehand in order to lower the resistance thereof, or ann-type impurity at a high concentration may be diffused after thepolycrystalline silicon film has been formed. Applicable as the materialof the silicide layers is any of molybdenum silicide (MoSi_(x)),tungsten silicide (WSi_(x)), tantalum silicide (TaSi_(x)), titaniumsilicide (TiSi_(x)), etc., and the silicide layers may well be formed inaccordance with a known method.

The lightly-doped drain (LDD) regions 107 of a p-channel FET 201 aredoped with boron (B) at a dose of 1×10¹³˜1×10¹⁴ [/cm²] as an impurityelement which bestows the conductivity type of p-type. On the otherhand, the LDD regions 113 of an n-channel FET 202, and those 119 and 125of a switching FET 203 and a current controlling FET 204 made up ofn-channel FETs are doped with phosphorus (P) or arsenic (As) as theimpurity element which bestows n-type conductivity, at a dose similar tothat of p-type. These LDD regions are respectively formed inself-alignment in accordance with ion implantation or ion doping byemploying the corresponding gates as masks.

Side wall spacers 112, 118, 124 and 130 are formed in such a way that,after the formation of the LDD regions, an insulating film such assilicon oxide film or silicon nitride film is formed on the wholesurface of the resulting substrate by CVD, and that the insulating filmis uniformly etched over the whole area thereof by anisotropic dryetching, so as to be left behind on the side walls of the correspondinggates. The source regions and drain regions of the respective FETs areformed by employing the corresponding side wall spacers as masks. Morespecifically, the source region 108 and drain region 109 of thep-channel FET 201 is formed by ion-implanting boron (B) at a dose of5×10¹⁴˜1×10¹⁶ [/cm²]. The n-channel FET 202, and the switching FET 203and current controlling FET 204 made up of these n-channel FETs arerespectively formed with the source regions 114, 120 and 126 and drainregions 115, 121 and 127 by ion-implanting arsenic (As) at a dose of5×10¹⁴˜1×10¹⁶ [/cm²].

A first interlayer insulating film 131 is formed to a thickness of100˜2000 nm out of a silicon oxide film, an oxidized silicon nitridefilm or the like which should preferably be prepared by plasma CVD orlow-pressure CVD. Further, the first interlayer insulating film 131 isoverlaid with a second interlayer insulating film 132 which is made ofphosphosilicate glass (PSG), borosilicate glass (BSG) orphosphoborosilicate glass (PBSG). The second interlayer insulating film132 is prepared by spin coating or normal-pressure CVD. The preparedfilm is caused to reflow by a treatment of thermal activation at 700˜900[° C.], which is carried out after the preparation and which serves alsoas a heat treatment, whereby the surface of the second interlayerinsulating film 132 is flattened.

Source wiring lines 133, 135, 137 and 139 and drain wiring lines 134,136, 138 and 140 are respectively formed after contact holes reachingthe source regions and drain regions of the corresponding FETs areformed in the first interlayer insulating film 131 and the flattenedfilm 132. Aluminum (Al) which is usually and often used as alow-resistance material, may be employed for the wiring lines.Alternatively, a multilayer structure consisting of an Al layer and atitanium (Ti) layer may be employed for each of the wiring lines.

A passivation film 141 is formed of a silicon nitride film, a siliconoxide film or a nitrified silicon oxide film by plasma CVD. Further, athird interlayer insulating film 142 is formed of an organic resinmaterial to a thickness of 1 [μ m]˜2 [μ m]. Any of the following: apolyimide resin, a polyamide resin, an acrylic resin, benzo-cyclo-butene(BCB), etc. can be used as the organic resin material. The merits of theuse of the organic resin material are that a method of forming the filmis simple, that parasitic capacitance can be lowered owing to a lowrelative dielectric constant, that the material is suited to beflattened, and so forth. Of course, any organic resin film other thanmentioned above may be employed. Here, the polyimide resin of the typewhich is applied on the resulting substrate and then is treated bythermal polymerization is employed, and it is baked at 300 [° C.] in aclean oven.

A pixel electrode 143 is connected to the drain wiring line of thecurrent controlling FET 204. The pixel electrode 143 is formed of alow-resistivity material typified by Al. An Al film can be readilyformed by a known method of forming the film, for example, vacuumdeposition or sputtering. In order to improve the contrast, the surfaceof the pixel electrode 143 may be roughened into a diffusing reflectivesurface.

After the formation of the pixel electrodes 143, cathode layers 144containing a metal of low work function are formed on all the pixelelectrodes. Since the cathode layer 144 is as thin as a few nm or so,whether a true layer is formed or it exists sporadically in the shape ofislands is unclear, and hence, its contour is indicated by a brokenline.

A material which is usable as the cathode layer 144 containing the metalof low work function, is lithium fluoride (LiF), lithium oxide (Li₂O),barium fluoride (BaF₂), barium oxide (BaO), calcium fluoride (CaF₂),calcium oxide (CaO), strontium oxide (SrO) or cesium oxide (Cs₂O). Sincethe material is insulating, the short-circuiting between the pixelelectrodes is not incurred even when the cathode layer 144 is aconnecting layer. Of course, a cathode layer made of a known materialhaving conductivity, such as MgAg electrode, can be used as the cathodelayer. It is necessary, however, to form cathodes themselves selectivelyor to perform patterning, so as to prevent the pixel electrodes fromshort-circuiting.

An organic EL (electroluminescent) layer 145 is formed on the cathodelayer 144 containing the metal of low work function. Although a knownmaterial or structure can be employed for the organic EL layer 145, amaterial capable of white luminescence is used in the present invention.Structurally, the organic EL layer 145 may be formed of nothing but aluminescent layer which offers a site for recombination. If necessary,it is also allowed to stack on this an electron injection layer, anelectron transport layer, a hole transport layer, an electron blockinglayer, a hole blocking layer or a hole injection layer. Here in thisspecification, all the layers where carriers are injected, transportedor recombined shall be comprehensively called the “organic EL layer”.

In addition, the organic EL material used for the organic EL layer 145is a high-molecular one based on a polymer. For example, the organic ELlayer 145 is formed in such a way that PVK (polyvinyl carbazole), Bu-PBD(2-(4′-tert-butylphenyl)-5-(4″-biphenyl)-1,3,4-oxadiazole), coumarin 6,DCM 1 (4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran),TPB (tetraphenylbutadiene) and Nile red are dissolved in1,2-dichloromethane or chloroform, and that a solution thus obtained isapplied by spin coating. The substrate structure coated with thesolution is rotated at a rotational frequency of about 500˜1000 [rpm]for 20˜60 [seconds], whereby a uniform coating film is formed.

Of course, the coating film is formed after the organic EL material isrefined (typically, by dialyzing) at least 3 times, preferably 5 timesor more, thereby to lower the sodium content of this material to 0.1[ppm] or less (preferably, 0.01 [ppm] or less). Thus, the sodium contentof the organic EL layer 145 becomes 0.1 [ppm] or less (preferably, 0.01[ppm] or less), and the volume resistance thereof becomes 1×10¹¹˜1×10¹²[Ωcm] (preferably, 1×10¹²˜1×10¹³ [Ωcm].

The organic EL layer 145 formed in this way is overlaid with atransparent conductive film as an anode layer 146. Usable for thetransparent conductive film is a compound (called “ITO”) produced fromindium oxide and tin oxide, a compound produced from indium oxide andzinc oxide, tin oxide (SnO₂), zinc oxide (ZnO), or the like.

Besides, the anode layer 146 is overlaid with an insulating film as apassivation film 147. The passivation film 147 should preferably be asilicon nitride film or a nitrified silicon oxide film (expressed by“SiO_(x)N_(y)”).

The substrate structure completed up to this point in this specificationshall be called “active matrix substrate”. That is, the “active matrixsubstrate” is the substrate which is formed with the FETs, the pixelelectrodes electrically connected to the FETs, and organic EL elementsincluding pixel electrodes as the cathodes (capacitors consisting of thecathode layers, the organic EL layer and the anodes).

FIG. 2(A) is a top plan view of the pixel unit of the active matrixsubstrate, while FIG. 2(B) is a connection diaphragm of the circuitarrangement of the pixel unit. In actuality, the pixel unit (imagedisplay unit) is so constructed that a plurality of pixels are arrayedin the shape of a matrix. Incidentally, a sectional view taken alongA-A′ in FIG. 2(A) corresponds to the sectional view of the pixel unit inFIG. 1. Accordingly, common reference numbers are indicated in FIG. 1and FIG. 2(A), both of which may be referred to on occasion. Besides,two pixels are illustrated in the top plan view of FIG. 2(A), and theyhave the same structure. As shown in FIG. 2(B), two FETs per pixel aredisposed for the organic EL element 205. Both the FETs are of n-channeltype, and they function as the switching FET 203 and the currentcontrolling FET 204. Reference numeral 149 designates a gate wiring.

In the above way, upon the single-crystal silicon substrate can beformed driver circuits each of which is based on a CMOS circuitconfigured with a p-channel FET 201 and a n-channel FET 202, and pixelunits each of which includes switching FET 203 and current controllingFET 204 formed of n-channel FETs. The driver circuits based on the CMOScircuits can form, for example, a shift register circuit, a buffercircuit, a sampling circuit, a D/A converter, and a latch circuit. Sincesuch circuits are constructed of the insulated-gate FETs whose activelayers are made of single-crystal silicon, they are capable ofhigh-speed operations, and a lower power consumption can be achieved bysetting their drive voltages at 3˜5 [V]. By the way, the structures ofthe FETs explained in this embodiment are nothing more than mereexamples, and the FETs need not be restricted to the structures shown inFIG. 1.

FIG. 3 is a top plan view showing an active matrix substrate. Referringto the figure, the active matrix substrate includes a substrate 1000, apixel unit 1001, data line side driver circuits 1003, and scanning lineside driver circuits 1002. Input terminals for the respective drivercircuits are pads 1006 for wire bonding which are disposed near theedges of the substrate 1000, and they are connected to the drivercircuits via leads 1004˜1005. The pixel unit having a size of from0.5-inch class to 2.5-inch class is well suited for fabrication.

The active matrix substrate formed with the organic EL layer is sealedin a package in order to be cut off from external shocks, and ambientconditions such as dust and humidity. The shape and scheme of thepackage are exemplified in FIG. 4. A bed plate 401 is formed of aninsulating material such as ceramics, and the active matrix substrate413 formed with the organic EL layer is fixed thereon by a low-meltingglass or metallized layer 402. The active matrix substrate 413 isconnected with an external circuit by a lead frame 403, which isconnected with the active matrix substrate 413 by wire pieces 412 ofgold (Au) through pads 410 for wire bonding.

The active matrix substrate 413 is sealed with a cover ceramic plate405. The ceramic cover plate 405 is bonded with the bed plate 401 by abinder layer 404. Pyroceram cement, bismuth oxide-based glass, leadoxide-based glass, or the like is used for the binder layer 404. Awindow member 406 made of a transparent quartz plate, a transparentglass plate or the like is mounted and fixed with adhesives 407 in anarea where the cover plate 405 formed of the ceramics or the likeinsulating material similarly to the bed plate 401 lies over the pixelunit of the active matrix substrate 413. In this way, the active matrixsubstrate 413 formed with the organic EL layer is enclosed, and a vacantspace 414 is formed. Further, the vacant space 414 should desirably befilled with an inert gas (such as argon, helium, krypton, xenon ornitrogen) or have a drying agent (such as barium oxide) put therein. Inthis way it is possible to suppress the deterioration of the EL elementattributed to moisture etc.

Although not shown in this embodiment, a color display can also beconstructed by disposing color filters or black matrix layers (lightintercepting layers) on the organic EL layer in correspondence with theindividual pixels formed from the organic EL layer of the active matrixsubstrate. Alternatively, color filters may well be disposed at thewindow 406 shown in FIG. 4.

In the state shown in FIG. 4 as described above, the lead frame 403 isconnected to the terminals of the external equipment, whereby an imagesignal etc. can be inputted to display an image on the pixel unit. Herein this specification, an article which is brought into a state where itis capable of displaying an image, by attaching a lead frame to anexternal circuit, is defined as an “organic EL display device”.

Now, there will be described a practicable example in which an organicEL display device of active matrix type is applied to a goggle typedisplay device. FIG. 5 shows a schematic view of the goggle type displaydevice in this example. The goggle type display device main body 3600 isfurnished with two, right and left display units, which are constructedof organic EL display devices 3602R, 3602L, circuit boards 3603R, 3603Land lenses 3601R, 3601L.

FIG. 6(A) shows a sectional view of part A indicated in FIG. 5, whileFIG. 6(B) shows an enlarged view of part B indicated in FIG. 6(A). Asshown in FIGS. 6(A) and 6(B), in this example, in the goggle typedisplay device 3600 the organic EL display device 3602R mounted on thelens 3601R is connected to the circuit board 3603R equipped with asignal control circuit etc., through a lead frame 3606R. Lightluminescing from the organic EL display device 3602R arrives at theeyeball 3604R of the user via an optical path indicated by arrows inFIG. 6(A), whereby the user can recognize an image. Reference numeral3607R designates a sealing material.

The organic EL display device has a wide view angle owing to itsspontaneous luminescence. When applied to the goggle type displaydevice, the organic EL display is not spoilt even if the relativepositions of this display device and an observer's eye have deviated.

The present invention brings forth an effect as stated below:

A single-crystal semiconductor substrate which is formed withinsulated-gate field effect transistors and an EL layer, is held in avacant space which is defined by a bed plate and a cover plate formed ofan insulating material, and a packing material for bonding the bed andcover plates, and the vacant space is filled with an inert gas and adrying agent, whereby the oxidation of the EL layer can be prevented toprovide an organic EL display device of high reliability.

What is claimed is:
 1. A goggle type display device comprising: firstand second light emitting devices, each of which includes a singlecrystal semiconductor substrate; first and second insulated gate fieldeffect transistors provided on the single crystal semiconductorsubstrate; a field oxide film isolates the first insulated gate fieldeffect transistor from the second insulated gate field effecttransistor; an EL layer comprising an organic material provided over theinsulated gate field effect transistors; color filters over the ELlayer; a source wiring line electrically connected to the firstinsulated gate field effect transistor; a passivation film comprisingsilicon nitride over the EL layer; a first plate and a second plateformed of an insulating material; a first lens corresponding to thesecond plate of the first light emitting device; and a second lenscorresponding to the second plate of the second light emitting device,wherein the EL layer emits a white light, and wherein the source wiringline and the field oxide film overlap each other.
 2. The goggle typedisplay device according to claim 1, wherein the single crystalsemiconductor substrate is held in a space which is defined by the firstplate and the second plate.
 3. The goggle type display device accordingto claim 1, wherein the single crystal semiconductor substrate includesn-wells.
 4. The goggle type display device according to claim 1, furthercomprising: light intercepting layers over the EL layer.
 5. A goggletype display device comprising: first and second light emitting devices,each of which includes a single crystal semiconductor substrate; firstand second insulated gate field effect transistors provided on thesingle crystal semiconductor substrate; a field oxide film isolates thefirst insulated gate field effect transistor from the second insulatedgate field effect transistor; a pixel electrode over the insulated gatefield effect transistors; an EL layer comprising an organic materialprovided over the pixel electrode; color filters over the EL layer; asource wiring line electrically connected to the first insulated gatefield effect transistor; a passivation film comprising silicon nitrideover the EL layer; a first plate and a second plate formed of aninsulating material; a first lens corresponding to the second plate ofthe first light emitting device; and a second lens corresponding to thesecond plate of the second light emitting device, wherein the EL layeremits a white light, and wherein the source wiring line and the fieldoxide film overlap each other.
 6. The goggle type display deviceaccording to claim 5, wherein the single crystal semiconductor substrateis held in a space which is defined by the first plate and the secondplate.
 7. The goggle type display device according to claim 5, whereinthe single crystal semiconductor substrate includes n-wells.
 8. Thegoggle type display device according to claim 5, further comprising:light intercepting layers over the EL layer.
 9. The goggle type displaydevice according to claim 5, wherein the pixel electrode has a diffusingreflective surface.